Radio direction finding



June 23', 1936. E. J. HEFELE 2,044,789

RADIO DIRECTION FINDiNG Filed June 17, 1932 -5 Sheets-Sheet 1 Rad/o V .5 6'3 52 R ad/o J R ceiving I G/rc m a 40 INVENTOR ATTORNEY B EWARD J. Q

June 23, 1936. EQJ. HEFELE RADIO DIRECTION FINDING Filed June 17, 1932 5 Sheets-Sheet 2 R n v'qvr-un. n n uonom a g v hu AA I VIV VII" INVENTOR 5 EDWARD J. HEFBLE II to cmrflfimsly III III/llqmfHE- er Spare Calf/mar M ATI'ORNEY lie 23, 1936. E. J. HEFELE 2,044,739

RADIO DIRECTION FINDING Filed June 17,1932 5 Sheets-Sheet 5 INVENTOR' EDWARD J. HEFELE ATTORNEY .Eume 23 N36. E. J. HEFELE 2,044,789

RADIO DIRECTION FI-NDI'NG Filed June 17, 1952 5 Sheets-Sheet 5 I I i l I l I l g x I, I I I i a I l x l I I I g I I III I g l I, I I I I I l INVENTOR EDW RD 3. UEFEL ATTORNEY Patented June 23, 1936 Luu'r-si) STATES- RADIO mnso'rron moms Edward Joseph Heme. Lindenhurst. N. Y., as-

signor to Airp lane and -Marine Direction Finder 00.. Hndenhurst, N. in, a corporation of Delaware Application rune'ir, 1932, Serial a... 617,793 k a tilaims. (c1. ass-.41)

My invention relates to apparatus ior and methods of operating radio receiving systems;

and more particularly to apparatus for and methods of operating directional receiving systems used in direction finding and distance determination.

An object of the invention is'to providenovel means for and methods of improving the directional characteristic of radio receiving systems, beyond that obtainable from the absorbing element itself.

Another object of the invention is to provide novel means forgand methods of improving the directional sensitivity beyond that obtainable from the antenna itself of radio direction finders method; 1 s 7 Still another object the invention is" to pro= vide novel means for and method of obtaining as great a directional sensitivity when utilizing the maximum signal method as heretofore ob tainable with the minimum or null signal method.

A further object of the invention is to provide utilizing either the maximum or minimum signal novel means for securing any predetermined relation between the input and output voltages of a radio receiver used in determining direction or distance.

Still a further object is to provide novel means ior varying the rate of change of the output volt- -age with respect to a predetermined rate of change of the input voltage in directional rad! receiving systems.

A specific object of the invention, is to provide novel means for securing any predetermined nonlinear relationship between input and output voltages oi a directional radio receiving system. A'still further object of the invention is to secure this result either in the receiver itself.

in its associated indicator, or by a combination of the two.

. Another object of the invention is accomplish this result in radio direction finding or distance indicating receivers by means of automatic gain control, or by utilizing variableimu" ..the'detailed description of the invention given hereinafter.

Directional reception depends upon the nonceiving system.

' Another form of uni-directional antenna, comsitivity is correspondingly great.

uniform directional absorbing power of an entenna. In polar coordinates, this characteristic is expressed by any diagram other than one having a constant radius.

The most common form of a directional an- '5 terms. is the simple loop or symmetrical dipole.

Its directional characteristic is expressed in polar coordinates by a figure 8 pattern. ,That is, the electromotive force induced in such an antenna when used for receiving radiant energy 10 varies ,with the angular position of the antenna and direction as thecosine of the angle.

Another familiar form of directional antenna consistsoi' a combination of a loop and nondirectional vertical antenna. Its characteristic )5 describes in polar coordinates a curve known as the cardioiol or heart-shaped diagram. This system is known in the art as a uni-directional remonly used in reception of short waves, consists 01' a series of spaced conductors or-antennse form. ing a so-called antenna array". Its directional sensitivity is great in a given direction and small in all other directions and is expressed in polar coordinates by an elongated or exaggerated el ipse. Y

.As described above, the directional characteristics depend on the change of radii in the polar v diagram of the antenna. When the rate oi change of the, radii is great, the directional se'n- Inasmuch as the rate of change of the radii is quite considerable at or near the null position and is very I slight at or near the maximum position, the null method of direction finding has been used in preference tothe maximum method. r

To state this as applied to practical long wave direction finding, the accuracy of observation de pends upon; the sensitivity of the indicator to small changes in the electromotive iorc'e impressed upon it. This eleotromotlve i'orce varies with the angular rotation of the loop antenna used in such systems and is normally expressed by a sine curve in rectangular coordinates and by a figure 8 pattern, harmed by two tangential circles of equal diameter, in polar coordinates. v

This characteristic figure8 pattern is used .in direction finding bynoting the direction-of the loop antenna either when the signals are loudest or weakest; the former is known as the maximum method and the latter as the or null method 01' direction finding. From an inspection or the normal figure-s5 8 pattern, it will be observed thatvfor maximum signals, the radius of curvature is large so that there is a small rate of change of output voltage with variation in angular position of the loop antenna. For minimum signals, the radius of curvature is small and, "accordingly, there is a large rate of change of output voltage and variation in angular position of the loop antenna.

I have discovered that this rate of change obtained in the output of the receiver for both the maximum and for the minimum positions may be accentuated by varying the input-output voltage relationship in the receiving system or at the indicator or by a combination of both. This then correspondingly accentuates the over-all characteristic of the entire system and increases the sensitivity of the readings at either the maximum or minimum positions.

When the null method is used, the figure 8 pattern is flattened by causing the input-output relationship of either the receiver, or indicator, or both, to vary non-linearly and in accordance with the expression:

the receiver or indicator or both to vary nonlinearly and in accordance with the expression:

where e'=input voltage, E=output voltage, Ae=increment in input voltage, AE=increment in output voltage, and X is some variable that approaches infinity as e increases; that is,. the rate of change of output with respect to rate of change of input is made such that the ratio oi rate of change of output to rate of change of input becomes larger as the input is increased.

Theinvention will be made clearer from the detailed description following, in connection with the drawings in which:

- Figure 1 is a circuit diagram of one embodiment of the invention.

Figure 2 is a modified form of my invention in which saturated transformers are used to carry out my invention. v

Figure 3 is a curve drawn to polar coordinates showing the relationship between the variousangular positions of a directional or loop antenna and the signal intensity as indicated on an output meter of the type described, in a system utilizing my invention.

Figure 4 is a modified form of my invention disclosing the use of automatic gain control in a receiver used indirection findingQ Figure 5 shows the curves of resistance to current density of copper oxide rectifiers used in one form of my invention. I

Figure 6 consists of curves showing the instrument calibrations used in my invention.

Figure '7 illustrates the usual form of indicatresponse curve heretofore used for direction find- ,mum is obtainable. In fact, there is no sharply automatic gain control.

ing instrument heretofore used in direction finder systems.

Figures 8 and 9 are diagrammatic views of my preferred form of indicating instrument, Figure 8 being used for maximum method and Figure 9 for null method operation.

Figures 10 to 27 are curves in both polar and linear coordinates showing the relation between antenna energy and indicator response obtained by using this improved system. 10

Figure 28 is a diagrammatic illustration of the change in wave shape of the received signal as it passes through the receiver to the indicator.

Figure 29 is aseries of curves drawn to rectangular coordinates showing the shape of the signal waves for different exponential values.

Referring to the drawings, I have illustrated in Figure 10 the figure 8 pattern drawn to polar coordinates illustrating the relationship between various angular positions of the loop and the energy absorbed; and in Figure 11 I have shown the same relationship drawn to rectangular'coordinates.

As has already been explained, the normal loop 0 ing'may be represented either as a figure 8 consisting of two tangential circles of equal diameter as shown in Figure 10, or by a sine curve, as shown in Figure 11.

A similar figure 8 is obtained in the output of the radio receiver when the rate of change of the output voltage with respect. .to the rate of change of input voltage is constant, as expressed in the Equation (1) when X=constant k, and illustrated in Figure 12.

In this case, the curve of Figure 12 is a straight v line so that the response of an indicator such as shown in Figure 7, connected to the output of the radio receiver, varies directly with the voltage applied to the radio receiver as indicated in Figures 14 and 15. Because the curvature is steep at or near the null position, the response is sharp, as indicated in Figure 13. This latter figure is drawn to rectangular coordinates and indicates the over-all response of the loop, receiver, and indicator for various angular positions of the antenna near the null. It has substantially the shape of the sine curve shown in Figure 13, the lower half of the wave being turned back on itself to indicate more clearly the sharpness of re.- sponse.

In the case described above, a radio receiver having a straight line amplifying characteristic is used and a very much sharper null than a maxidefined maximum position.

In accordance with my invention, radio circuits and receivers are employed to produce a more sharply defined null position or, altemateiy, a sharply defined maximum position. In one embodiment of this invention, it is accomplished by utilizing circuits having non-linear amplifying characteristics as, for example, by employing automatic gain control and variable mu tubes.

In Figure 4, there 'is disclosed one form of As will be well understood, input energy from a directional antenna (not shown) is applied across the control electrode of the first tube I through the tuned circult 2, comprising the inductance l and variable condenser 4 connected across the loop. The out-' i put from the tube I is applied through the transformer I! to the input of a detector or demoduto an audio frequency amplifying circuit 8, and

plate current and efiectively biases the grid of the p tube 8- in accordance with the carrier strength. To accomplish this, the cathode bias resistor is of the detector tube 6 has developed across it a voltage which increases as the carrier increases.

As the potential applied across the input of the first tube increases, the'gain control functions to decrease the amplifying characteristic by changing the grid potential-of the tube 8. Similarly, other tubes than i may be controlled by this system if desired.

With this arrangement, the amplification characteristic or gain of" the radio receiver becomes non-linear; that is to say, as expressed in Formula (1), X approaches zero since the gain is high for low voltage input and decreases as the input voltage increases. This describes a curve, Figure 18. The resulting figure 8 is the deformed or flattened figure, illustrated in Figure 20. The steepness of curvature at or near the null position has been considerably increased and is o illustrated to better advantage by the rectilinear coordinate Figure 21. This increased steepness of curvature at the null has of course resulted in an increased flattening of the curve at its maximum. Thus, the system has become more sensitive at or near the null and less sensitive at the maximum than has been heretofore obtained.

A sharpened null position response curve is indicated by Figure 19 wherein the indicator re- I an exponential or logarithmic law as follows:

Where X is less than 1, an exponential Equation (3) is obtained. v I

Where X is greater than i, a logaritc Equation (4) output=6Xinput Eoutput=L0ga8input is obtained.

Both the above conform to the general eonditions stated in Equation (1).

This characteristic can be further accentuated by the combination of variable mu tubes and automatic gain control.

Although only one form of automatic gain control has been described for purposes of illustration, other forms or automatic gain control may be used in this invention.

Thus, for example, other well known automatic gain control systems may be used in inverted relation so that the gain of the receiver increases with increase in voltageimpressed across the receiver. The gain or the radio receiver will then be low tor low voltage inputs and high for the defined. A more sensitive response at the maxihigh voltage inputs, producing a response curve.

as shown in Figure 24.

' The figure 8 pattern is elongated as shown in Figure 26 so that the receivingcircuit's sensitivity at the maximum is much greater than in 5 Figure 14 and particularly the flattened figure} I pattern of Figure 20.- This is more clearly shown when drawn to rectangular coordinates in Figure 21, wherein the maximum islshown sharply 10 mum is thus obtained at the expense of sensitivity at the null as shown diagrammatically in Figure-25. v

In the above, circuitarrangements have been described for increasing the sensitivity at the null and at the maximum. As is wellunderstood, the maximum method is much preferred to the null method but has not been extensively used because of lack of clear definition of the maximum. According to this invention; the maximum 20,

in a manner now well known in the art. The I tuned antenna circuit is connected across the in- 3 put terminals of a radio frequency amplifier, the output of which is connected to a detector which in turn is connected to an audio frequency amplifier This is now well known in the art and accordingly is illustrated diagrammatically. 35 Theoutput current from the audio frequency amplifier is applied in turn through the system oi rectifiers it to the indicating instrument 55. As shown, the rectifiers 7 H, which may be oi! the copper oxide type, are connected in a Wheatstone bridge arrangement, the indicating instrument iii being connected across the bridge. The positive half of the pulsating current in the output circuit oi the audio frequency amplifier'fiows through. the rectifier system it, in one direction only to as the instrument as. The negative half of the pulsating current flows from the output of the audio frequency amplifier through the rectifier itin the opposite direction and in the same direction as the first hali cycle through the instrument it. Both halves of the rectified currents thus flow through the instrument E5 in the same direction.

Because of the comparatively large power consumption and delicacy of alternating current measuring instruments, such as thermal, iron vein and dvnamometer types, measuring instruments for direction finding equipment are inherently confined to the, direct current rectifier types. These have been found to be more ru ged. producing full scale deflection with currents of l to 2 milliamperes. These output measuring instruments are connected to the radio receiving circuit" through a rectifier as, for example, vacuum tube type or copper oxide type of rectiile'rs. However, the resistance or solid rectifiers change for difierent current densities per square centimeter of rectifier; the resistances being quite large for current densities in milliamperes per square centimeter, decreasing rapidly as the cur-= rentdensity is increased at first and thereafter 7o decreasing slowly.

Thus, as shown by the curve in Figure 5, as the current through the rectifier is increased from 0 to! or 5 milliamperes, per square centimeter. the

rectifier resistance decreases-first very 3 then more slowly from infinity to about 800 or 1000 total instrument resistance.

ohms for-a th inch rectifier. As the current is further increased to 50 or 60 milliamperes per square centimeter, the resistance falls more and more slowly to about 500 to 600 ohms.

Inasmuch as the scale of the instrument connected to the rectifier depends upon the relation of its resistance to the'resistance of the rectifier,

this change in ohmic resistance with a change of current density flow through the rectifier must be taken into consideration. The rectifier type of alternating current instruments are found to have a true uniform scale only when the resistance of I the rectifier unit forms a negligible part of the As the rectifier resistance approaches the instrument resistance in value, the lower end of the scale becomes somewhat crowded or narrowed.

For example, in the case of a 5 volt instrument of 1000 ohms per volt sensitivity, the current flowing through the rectifier at full scale deflection is 1 milliampere. For this current, the rectifler resistance is in the vicinity of 1000 ohms. But

at one volt when the currentthrough the' rectifier is only about a fifth of .a milliampere, the rectifier resistance is 2000 ohms. Therefore, for one volt, the total instrumentresistance has increased from 5000 to 6000 ohms. The impressed potential of one volt will'therefore cause less than one-fifth of the deflection produced by the five volts.

'In voltmeters with ranges of about 15 volts and with reasonably high sensitivity, the non linearity hereinbefore explained with the null method, the

near zero' indications should possess maximum sensitivity and instead of one-quarter of the scale measuring a third of the full scale voltage changes,

' the exact converse is desired.

This is obtained by constructing the indicating instrument as shown in Figure 9. As shown, there is provided a pivotal armature I5 carrying a pointer I6 operating over a graduated scale In operative relation with the armature l5 there are provided two pole-pieces l8 and I9. pole-pieces i8 and I9 are pivotally mounted, as shown at 20 and 2|. The edges 22 and 23 of the pole-pieces I8 and I9 opposite their faces 2| and 25 are in engaging relation with the pole exten-- sion 26 which completes the magnetic circuit through the armature and airgap.

Pole-pieces l8 and I9 may be angularly displaced about their pivots 20 and 2| to any desired degree in either direction by a manual adjusting screw or lever connected thereto. Preferably pole pieces l8 and I9 are controlled simultaneously by a common member, as for example 21; so that the two pole pieces will be displaced clockwise or counter-clockwise simultaneously and through the same angular displacement.

Thus, for example, the pole-pieces may be made to assume theposition shown in'Fi'gure 9 in which the lower end of the pole-piece I8 has been moved away to increase its airgap. Simultaneously, the pole-piece 2| has been displaced so that its upper end has been brought close to the armature to reduce the airgap therebetween while the lower end has been moved away to increase the airgap there;

It should be noted that theedges z: and a are These sloped to form the arc of a circle with 20 as its center andthat the edge or the'pole-piece 26 in cooperation therewith has-a similar are shaped I edge so that as the pole pieces 22 and 23 are moved about their pivots 2|, the edges 22 and 23 remain 5 continually in engaging relation with the polepiece 26 to maintain a minimum reluctance of this magnetic path thereat.-

With the pole pieces rocked, as shown in Figure 9, and the gaps at the edges 28 and 3| reduced to 10 a minimum, the reluctance of the magnetic path including the pole-pieceaarmature, and the airgaps, is a minimum while the pointer deflection is near zero.

When now the current through the receiving 15 instrument is increased slightly, there is a change in the magnetic lines of force which produces a corresponding deflection of the pointer through a predetermined angle in accordance with the change in current flow. 20 Assuming now that the instrument pointer is nearer the end of the scale at its maximum deflected position, the armature is now in the 'position opposite the pole ends 29 and 30 where the gap is at a maximum. A corresponding change '25 in current flow through the instrument at this position will not produce as large a change in the magnetic lines of force and accordinglythe change in deflection for this change of current will not be aslarge as was the case for a similar change 30 The characteristic of the rectifier by which 40 its resistance decreases with increase in current density may be applied withadvantageto the maximum method of direction indication since in As illustrated in-Figure 8, the adjustment is oo such that the ends 29 and 30 are so placed as to secure a minimum airgap for maximum deflection and'a maximum airgap for zero deflection. The instrument then responds exponentially where X is greater than 1. 55

The type of indicator shown in Figures"! to 9 may be usedwith the usual type of radio receiver as shown, for producing either a logarithmic or exponential response; or ii desired, may be used with special circuits for exaggerating these efi'ects. Thus, the logarithmic indicator, Figure 9, may be used with a sensitivity control circuit including variable mu tubes as shown in Figure 4 for producing logarithmic response, or an exponental response to a more negative power. The exponential indicator of. Figure 8 may be used with an exponential receiving circuit to produce higher powered exponential response than obtainable by either receiver or indicator individually. Although visual indicators are shown, it will be obvious to those skilled in the art that audible signal indicators may be used.

Figure 29 discloses a family of curves drawn to rectilinear coordinates. These curves illustrate how the normal response-mine may be dilresistance.

Q accuse by the use oi the exponential law alone, as given below:

output= hput inwhichxmaybeequal togreterthanorless than unity. The case in which x is greater than unity corresponds'to the Equation (2) and the case in which X is less than unity corresponds to Equation (1) Curve e is a pure sine wave obtained when x=-.1 and is the output obtained in the directional systems heretofore used, when connected to a normal loop and a linear indicator. Curves I, 9, It, show how the receiver output according to the invention is distorted to increase the null sensitivity by Equation 3 where X is equal to -2, -4

and 8, respectively.

Curves o, b, c, and 11 show how the receiver output is distorted to increase the maximum sensitivity by Equation & where x=1e, 8, 4, and 2, respectively.

In the following, the values used in plotting thme curves are tabled:

9 j c d c t o r;

I117 a" E" E E E 0 0 {E o o o c o 1 36.5 13.3 mt -.oa .ooo SIXIO- oixma n. 29.4 a1 .111 .0511 .003 9X10' 1o 04.5 41.5 17.38 a. .09 on 64Xl0' 20 10.4 sec 24.2 10.311 1.0a .012 .0014 so as. 70.6 50. as. on .at .0152 40 so. so. 64.28 41.5 11.11 s. .cs 50 93.5 87.2 1am to. as 12.1: 1.41 so. one saw 1a cos n 10.2 10 so one saw so. 1e 55. sun so so. as. sets 91.5 115. so. s1. s5 co. co. 99.62 seas 91.5 95. no. so cc. to. 99.935 cows var cs. cs5 to 100. 100. 100. 100. 100. 100. no.

Figure 2 illustrntm a further enema modification of my invention. in this Bin-..-". nent oi my 4 invention, o rotatable loop antenna and radio receiver circuit that descrim in con nection with-Flume l is employed. In place, however, of the special indicator, 2 provides. special transformer construction for producing a logarithmic response reading in a linear indienter. in cocci-dance with this embodiment I provide an oscillator such as, for example, a to cycle oscillator 6d connected across a @600 ohm nected in series, as shown, they'have the neces-' sary direct current resistance, to damp the gelvsnometerconstant with the rapid response and also have n, renctance not exceeding the direct current resistance oi the circuit.

By providing the proper ohmic resistance at ill in series withthe primary, the current in the primary oi the transformer is not ailfected by the a change in the magnetizationoi the core. The

secondary impedance is not-aflected by changes 15 g in magnetization of the core and the n Connected ocrosshii ohms thereoi high series impedance issupplied vby the galcurrent which flows in the saturation winding assuming no magnetic leakage; 5

a The current to be measured is received over the loop antenna I connected to the receiver 50.

The outputv from receiver 50 is, in turn, com

nected to the primary of transformer 5| the scondary oi which is in turn connected to the 10 anodes 01 a full wave gas filled rectifier tube such as tube :62. Tube 52 comprises an envelope enclosing anodes l3 and 58 and a common cathode Ii. The cathode is heated from a source 86 controlled by resistance 61. Extending from the mid-point of the secondary oi transformer ii is the lead 58 connected to the two auxiliary saturating windings 59 and 60 of transformers l8 and it, respectively. 1

' It is an obvious advantage to have no coupling between either the primary or secondary wind lugs and the saturation coil which might result. in the-latter feedlng baclr into its source ofsupply. Consequently, each primary and secondary may, ii. desired, be wound in two halves, one hell of each being assembled on each of the outer limbs of the transformer core.

The current in the transformer secondary from the oscillator 40 is increased and decreased as the amplitude of the measured current in wind= 30 ings B9 and Gil varies. As the measured current saturates the transformer. the induced currents in the secon ary from oscillator it decrease in primary amplitude. Accordingly, the indication of the galvanonieter varies inversely as the in- 35 put or measured current varies.

Figure 6 is a curve showing the d flection against log. 1, 1 being the variable currents opplied across the saturation coil from the full wave the preferred forms of radio receivers and indiso caters, itwill be obvious to those skilled in the art, that other means for and methods of varying the ratio of input voltage to output voltage may be employed and are part of my invention. Furthermore, my invention may be applied to 66 directional and distance finding systems as well. as direction finding, and I do not intend tolimit myself except as set forth in the appended claims.

I claim: p

i. In" a directional system including o direcso tional antenna, amplifier, and an indicator, the method of directional reception comprising receiving variableamounts of radiant energy in accordance with the position of the directional antenna with respect to the direction to the source to of said radiant energy; impressing the received energy across the input of the amplifier; amplii'ying the impressed energy in accordance with a non-linear exponential law such that as the input energy impressed on the amplifier from the 70 directional antenna varies in accordance with the direction of reception of the signal, the output of said amplifier will form a figure a which is substantially flattened as compared to the normal circle figure 8; and impressing said variable but- 76 4o duced by all positions of the directional antenna put signals from said amplifier directly on the indicator whereby the indicator response is more pronounced for predetermined changes in the input at the null of the figure 8 than in the case of a circular figure 8.

2. Ina directional system including a directional antenna, amplifier, and an indicator, the method or directional reception comprising re ceiving variable amounts of radiant energy in accordance with the position of the directional antenna with respect to the direction to the source of said radiant energy; impressing the received energy across the input of the amplifier; controlling the amplification by controlling the volume so as to amplify the impressed energy in accordance with a non-linear exponential lawv v the figure 8 than in the case of a circular figure8.

3. In a directional system, a directional antenna; anamplifying .circuit having an input and an output; means for connecting the input .01 said amplifier to said directional antenna;

said amplifier comprising means for impressing thereon variable amounts oi. radiant energy in accordance with the position of the directional antenna with respect to the direction to the source oi said radiant energy; said amplifier including means ior amplifying the impressed energy in accordance with a non-linear exponential law over the entire range of amplitude variations prosuch that as the input energy impressed on the amplifier from the directional antenna varies in accordance with the direction of reception of the signal the output of said amplifier will form a figureB which is substantially flattened as compared to the normal circle figure 8; an indicator; and means for impressing said variable output signals from said amplifier directly on the indicator whereby the indicator response is more pronounced for predetermined changes in the input at the null of the figure 8 than in the case of a circular figure 8.

4. In a directional system, a directional antenna; an amplifying circuit having an input and an output; means for connecting the input of said amplifier to said directional antenna; said amplifier comprising means for impressing thereon variable amounts of radiant energy in accordance with the position of the directional antenna with respect to the direction to the source of said radiant energy; said amplifier including means for controlling the amplification by volume control so as to amplify the'impressed energy in accordance with a non-linear exponential law over the entire range of amplitude variations produced by all positions of the directional antenna such that as the input energy impressed on the amplifier from the directional antenna varies in accordance with the direction of reception of the signal the output of said amplifier will form a figure 8 which is substantially flattened as compared to the normal circle figure 8; an indicator;

and means for impressing said variable output EDWARD JOSEPH HEF'ELE. 

